Programming a MIDI interface for Android

[MichaelListon]

Have a project to do for my final year in a computing degree, it can be pretty much anything so I've decided to try my hand at java programming for Android. I have an idea to create a simple interface which can send MIDI signals from the Phone via USB back to a DAW (Basically a clone of this http://createdigitalmusic.com/2009/06/android-midi-controller-musical-app-updates-with-midi-over-wifi/). I've been learning to program with Java for the last 3 years so I hopefully know enough to get by. Does anyone have any experience with MIDI programming on Android? Cheers!

[BCM]

not sure about this but isn't there some fundamental problem with Android and MIDI? in that it can't process it or something?

[mcbpete]

You can go a bit of a long way round using OSC i.e. Android to OSC to MIDI to PC, check out TouchOSC - http://hexler.net/software/touchosc-android . It's a bit of a faff but it works all the same (though I never did anything of use - couldn't get PureData, which happily (and wirelessly) accepted the OSC data from my HTC desire, to talk to Ableton)

[Guest]

I believe that Android has fundamental problems with DSP, but MIDI should be okay? Dunno if you can host USB-MIDI interfaces (as you can with the iPad & Camera Connection Kit), but even if there's no MIDI API already, you should be able to use the USB serial port to send and listen to a arbitrary byte stream. Then maybe clone the Arduino MIDI library: http://arduino.cc/pl...ain/MIDILibrary

 

Parsing MIDI is not rocket science, but a bit tricky nonetheless. Here's my convoluted ObjC implementation:

 

#define MD_MIDI_STATUS_SYSEX_BEGIN (0xF0)
#define MD_MIDI_STATUS_SYSEX_END (0xF7)
#define MD_MIDI_STATUS_CLOCK (0xF8)
#define MD_MIDI_STATUS_ACTIVESENSE (0xFE)
#define MD_MIDI_STATUS_NOTE_ON (0x90)
#define MD_MIDI_STATUS_NOTE_OFF (0x80)
#define MD_MIDI_STATUS_AFTERTOUCH (0xA0)
#define MD_MIDI_STATUS_CONTROL_CHANGE (0xB0)
#define MD_MIDI_STATUS_PROGRAM_CHANGE (0xC0)

#define MD_MIDI_STATUS_ANY (0x80)


#define sysexBufferSize (1024*1024)
uint8_t sysexBuffer[sysexBufferSize];
NSUInteger sysexBufferIndex = 0;

uint8_t noteOnBuffer[3];
NSUInteger noteOnBufferIndex = 0;

uint8_t noteOffBuffer[3];
NSUInteger noteOffBufferIndex = 0;

uint8_t aftertouchBuffer[3];
NSUInteger aftertouchBufferIndex = 0;

uint8_t ccBuffer[3];
NSUInteger ccBufferIndex = 0;

uint8_t programChangeBuffer[2];
NSUInteger programChangeBufferIndex = 0;


typedef enum receiveState
{
receiveState_None,
receiveState_Sysex,
receiveState_NoteOn,
receiveState_NoteOff,
receiveState_Aftertouch,
receiveState_ControlChange,
receiveState_ProgramChange,
}
receiveState;

receiveState _receiveState = receiveState_None;

@implementation MidiInputParser

- (void)midiSource:(PGMidiSource *)input midiReceived:(const MIDIPacketList *)list
{
//DLog(@"midi received..");
const MIDIPacket *currentPacket = &list->packet[0];

for (NSUInteger currentPacketIndex = 0; currentPacketIndex < list->numPackets; currentPacketIndex++)
{
for (NSUInteger currentByteIndex = 0; currentByteIndex < currentPacket->length; currentByteIndex++)
{
if(self.delegate)
{
unsigned char byteValue = currentPacket->data[currentByteIndex];

if(byteValue & MD_MIDI_STATUS_ANY) // got status byte
{
uint8_t hiNib = byteValue & 0xf0;

if(byteValue == MD_MIDI_STATUS_CLOCK) // check for realtime messages
{
// handle clock
}
else if(byteValue == MD_MIDI_STATUS_ACTIVESENSE)
{
// handle activesense
}
else if(byteValue == MD_MIDI_STATUS_SYSEX_BEGIN)
{
//DLog(@"sysex receive begin");
_receiveState = receiveState_Sysex;
// discard sysex buffer
sysexBufferIndex = 0;
sysexBuffer[sysexBufferIndex++] = byteValue;
}
else if (_receiveState == receiveState_Sysex && byteValue == MD_MIDI_STATUS_SYSEX_END) // sysex end (expected)
{
_receiveState = receiveState_None;
sysexBuffer[sysexBufferIndex++] = byteValue;
NSUInteger sysexDataLength = sysexBufferIndex;
sysexBufferIndex = 0;
if([self.delegate respondsToSelector:@selector(midiReceivedSysexData:fromSource:)])
{
@autoreleasepool
{
NSData *d = [NSData dataWithBytes:&sysexBuffer length:sysexDataLength];
[self.delegate midiReceivedSysexData:d fromSource:self.source];
}
}
}
else if (byteValue == MD_MIDI_STATUS_SYSEX_END) // unexpected sysex end (haven't started sysex receive)
{
;
}
else if (hiNib == MD_MIDI_STATUS_NOTE_ON)
{
_receiveState = receiveState_NoteOn;
noteOnBufferIndex = 0;
noteOnBuffer[noteOnBufferIndex++] = byteValue;
}
else if (hiNib == MD_MIDI_STATUS_NOTE_OFF)
{
_receiveState = receiveState_NoteOff;
noteOffBufferIndex = 0;
noteOffBuffer[noteOffBufferIndex++] = byteValue;
}
else if (hiNib == MD_MIDI_STATUS_CONTROL_CHANGE)
{
_receiveState = receiveState_ControlChange;
ccBufferIndex = 0;
ccBuffer[ccBufferIndex++] = byteValue;
}
else if (hiNib == MD_MIDI_STATUS_PROGRAM_CHANGE)
{
_receiveState = receiveState_ProgramChange;
programChangeBufferIndex = 0;
programChangeBuffer[programChangeBufferIndex++] = byteValue;
}
else if (hiNib == MD_MIDI_STATUS_AFTERTOUCH)
{
_receiveState = receiveState_Aftertouch;
aftertouchBufferIndex = 0;
aftertouchBuffer[aftertouchBufferIndex++] = byteValue;
}
else
{
NSString *type = @"unknown";
uint8_t loNib = byteValue & 0x0f;
if(hiNib == 0xD0) type = [NSString stringWithFormat:@"chan aftertouch @ chan %d", loNib];
else if(hiNib == 0xE0) type = [NSString stringWithFormat:@"pitch wheel range %d", loNib];
DLog(@"received unimplemented status byte: 0x%x type: %@", byteValue, type);
}
}
else
{
if(_receiveState == receiveState_Sysex)
{
// fill buffer
sysexBuffer[sysexBufferIndex++] = byteValue;
if(sysexBufferIndex >= sysexBufferSize)
{
DLog(@"overflowing sysex buffer, cancelling sysex receive.");
sysexBufferIndex = 0;
_receiveState = receiveState_None;
}
}
else if(_receiveState == receiveState_NoteOn)
{
//DLog(@"filling note on buffer..");
noteOnBuffer[noteOnBufferIndex++] = byteValue;
if(noteOnBufferIndex == 3)
{
_receiveState = receiveState_None;
noteOnBufferIndex = 0;
if((noteOnBuffer[2] & 0x7f) == 0 &&
[self.delegate respondsToSelector:@selector(midiReceivedNoteOff:fromSource:)]) // zero velocity note off
{
@autoreleasepool
{
MidiNoteOff *noteOff = [MidiNoteOff new];
noteOff.channel = noteOnBuffer[0] & 0x0f;
noteOff.note = noteOnBuffer[1] & 0x7f;
noteOff.velocity = noteOnBuffer[2] & 0x7f;
[self.delegate midiReceivedNoteOff:noteOff fromSource:self.source];
}
}
else if([self.delegate respondsToSelector:@selector(midiReceivedNoteOn:fromSource:)])
{
@autoreleasepool
{
MidiNoteOn *noteOn = [MidiNoteOn new];
noteOn.channel = noteOnBuffer[0] & 0x0f;
noteOn.note = noteOnBuffer[1] & 0x7f;
noteOn.velocity = noteOnBuffer[2] & 0x7f;
[self.delegate midiReceivedNoteOn:noteOn fromSource:self.source];
}
}
}
}
else if(_receiveState == receiveState_NoteOff)
{
//DLog(@"filling note on buffer..");
noteOffBuffer[noteOffBufferIndex++] = byteValue;
if(noteOffBufferIndex == 3)
{
_receiveState = receiveState_None;
noteOffBufferIndex = 0;
if([self.delegate respondsToSelector:@selector(midiReceivedNoteOff:fromSource:)])
{
@autoreleasepool
{
MidiNoteOff *noteOff = [MidiNoteOff new];
noteOff.channel = noteOffBuffer[0] & 0x0f;
noteOff.note = noteOffBuffer[1] & 0x7f;
noteOff.velocity = noteOffBuffer[2] & 0x7f;
[self.delegate midiReceivedNoteOff:noteOff fromSource:self.source];
}
}
}
}
else if(_receiveState == receiveState_ControlChange)
{
ccBuffer[ccBufferIndex++] = byteValue;
if(ccBufferIndex == 3)
{
_receiveState = receiveState_None;
ccBufferIndex = 0;
if([self.delegate respondsToSelector:@selector(midiReceivedControlChange:fromSource:)])
{
@autoreleasepool
{
MidiControlChange *cc = [MidiControlChange new];
cc.channel = ccBuffer[0] & 0x0f;
cc.parameter = ccBuffer[1] & 0x7f;
cc.ccValue = ccBuffer[2] & 0x7f;
[self.delegate midiReceivedControlChange:cc fromSource:self.source];
}
}
}
}
else if(_receiveState == receiveState_ProgramChange)
{
programChangeBuffer[programChangeBufferIndex++] = byteValue;
if(programChangeBufferIndex == 2)
{
_receiveState = receiveState_None;
programChangeBufferIndex = 0;
if([self.delegate respondsToSelector:@selector(midiReceivedProgramChange:fromSource:)])
{
@autoreleasepool
{
MidiProgramChange *pc = [MidiProgramChange new];
pc.channel = programChangeBuffer[0] & 0x0f;
pc.program = programChangeBuffer[1] & 0x7f;
[self.delegate midiReceivedProgramChange:pc fromSource:self.source];
}
}
}
}
else if(_receiveState == receiveState_Aftertouch)
{
//DLog(@"filling note on buffer..");
aftertouchBuffer[aftertouchBufferIndex++] = byteValue;
if(aftertouchBufferIndex == 3)
{
_receiveState = receiveState_None;
aftertouchBufferIndex = 0;
if([self.delegate respondsToSelector:@selector(midiReceivedAftertouch:fromSource:)])
{
@autoreleasepool
{
MidiAftertouch *aftertouch = [MidiAftertouch new];
aftertouch.channel = aftertouchBuffer[0] & 0x0f;
aftertouch.note = aftertouchBuffer[1] & 0x7f;
aftertouch.pressure = aftertouchBuffer[2] & 0x7f;
[self.delegate midiReceivedAftertouch:aftertouch fromSource:self.source];
}
}
}
}
}
}
}
currentPacket = MIDIPacketNext(currentPacket);
}
}

@end

 

 

It could probably be optimised a little, but when you look at the Arduino MIDI parser it looks just as messy, and it works so yeah :]

 

good luck & have fun.

 

edit: lol formatting

[oscillik]

audio code for DSP tasks was improved in Android 4.0, if that helps any...